Back fire trap for internal combustion engines



Feb. 6, 1934. o. A. CARNAHAN BACK FIRE TRAP FOR INTERNAL COMBUSTIbN ENGINES Filed May 22, 1930 INVENTOR. 01 2 6! 11 1 1 fiM/Z W' A TTORNEYJ.

Patented Feb. 6, 1934 UNITED STATES.

BACK FIRE TRAP FOR INTERNAL COMBUSTION ENGINES Orson A. Carnahan, Syracuse, N. Y.

Application May 22, 1930.

2 Claims.

This invention relates to back .fire traps for internal combustion engines andhas for its object a back fire trap which is particularly simple and economical in construction and highly l efficient in use.

The invention consists in the novel features and in the combinations and constructions hereinafter set forth and claimed. I

In describing this invention, reference is had :to the accompanying drawing in which like characters designate corresponding parts in all the views.

Figure l is an elevation of this backfire trap showing the same applied to a carburetor.

; Figure 2 is an end elevation thereof looking to the left of Figure 1.

Figure 3 is a fragmentary plan view of one of the strips.

Figures 4 and 5 are sectional views on lines 4-4 and 55, Figure 3.

Figures 6 and 7 are fragmentary views of another form of strip with projections, showing the projections arranged so that two like strips are arranged in layers or rolled up so that the projections of one will not nest with those of the other.

This back fire trap comprises, generally, a hollow body for connection to the air intake of the carburetor of the internal combustion engine and having an air intake opening and means for cooling the back fire comprising cooling strips or plates arranged in layers in the path of the air current passing into the carburetor through the body in order to be cooled so that when back fire ;:occurs, the hot back fire gases are cooled by contact with the plates when passing between them below the ignition point of any ignitable gases or oils about the outside of the engine or carburetor, these plates being spaced so close im-together that the body of the back fire gases is split up into thin sheets and the entire body of gas cooled throughout either by direct contact with the plates or by conduction from the portion of the gas which comes into contact with the plates. 1 designates the carburetor which may be of any suitable form, size and construction.

2 designates the body of the back fire trap, this having a neck 3 at one end for attachment to the 5Q -air intake pipe of the carburetor and having an opening 4 at its other end, the body between its open end and the neck is formed Venturi shape at 5 for a purpose to be hereinafter described. By

Venturi shape I mean that the curvature of the 5;;;interior walls resembles that of the throat of a Serial No. 454,800

Venturi tube. For any given flow through the back fire trap, this Venturi acts to increase the velocity from the large opening 4 towards the neck 3.

6 designates a body of flat strips or plates arranged in layers in the opening 4 of the body 1, which plates arespaced apart to formnarrow passages 'between them for permitting the inlet of the air and the'outlet of the back fire gases; The passages are sufficiently narrow. to cause the 5 cold strips or plates to cool the gases while they are passing outwardly between the plates or strips.

As here illustrated, the strips are arranged in layers by rolling them from the center out. and the strips or plates are spaced apart by the projections on opposite sides of the plates, the PI'O-r jections being struck from the strips leaving openings or depressions, that, is, the projection on one side leaves an opening or depression on the :other side of the strip and the projections on one side alternate with the projections on the other side, both lengthwise and transverse: ly of the strip.

'7 designates the projections on one side of the strip and 8 the depressions or openings left s by the projections on the other side of the strip and as seen in Figures 3, 4 and 5, the projections on one side alternate both lengthwise and transversely with the projections on the other side. When these projections and depressions are round or in other form and arrangement so that they will nest together, the strips are separated by plain strips or layers 9 so that the projections 7 and 8 engage at their tops with the faces of the plain strips 9. However, as seen in Figures 6 and 7, the projections may be so arranged at an incline or otherwise that the projections 10 on one strip will cross the depressions 11 on the next layer if they happen to come opposite each other. When the plain strip is omitted, the projections offer a sufiicient obstruction to the back fire gases so that they come into intimate contact with the plates and are cooled thereby.

The strips or plates are carried by a suitable 10p skeleton frame 12. The strips are first coiled about a central core or hub 13. After being wound, the hub is inserted in the frame and the hub secured to the frame by screws 14. The frame is secured in the open side of the body 1057 2 in any suitable manner as by screws 15.

In operation, normally the incoming air passes between the plates or strips and keeps them cool. When a back fire occurs, the heated back fire gases encounter the cold plates and the tioned reason alone, for other reasons includ ing the fact that the passages are narrow and therefore they cause skin friction, as well as the fact that the passage of the air between the strips introduces a turbulence just inside of the screening member. These facts cause the frame and strips to interpose considerable resistance to air flow. By increasing the area of the frame 12 the velocity between the strips is lowered for the same air flow and the resistance due to skin friction, etc., is cut down to a much larger degree proportionately than the relative increase in area. At the same time, the same quantity of air that passes through the strips must enter the carburetor air horn whose area is much smaller. It is necessary, therefore, to increase the velocity of the air flow, thus compensating for the decrease in area. This stepping up of velocity is accomplished by the venturi.

In the preferred form of my invention I arrange the curvature of the walls of the venturi so that the maximum curvaturec'omes at the point of lowest velocity and vice versa. Such an arrangement of curvature tends to produce continuous flow as distinguished from eddying flow.

Owing to the formation of the plates with the projections to space the plates or strips apart, the fire trap feature is particularly simple and economical in construction and can be readily applied to the body and attached to any shape either circular or non-circular.

What i claim is:

1. A back fire trap for internal combustion engines comprising a body for attachment to the air intake of the carburetor of the engine, the body beingopen at one end for the intake i Of air and the outlet of back fire gases and having a tubular outlet at its other end connectible to the intake of the carburetor, the open intake end being of greater diameter than the tubular outlet, means in the intake opening for cooling the back fire gases, the walls of the body between the intake end and the tubular outlet curving in an outward curve from the intake end toward the tubular outlet to the intermediate part of the body and then curving in an inward reverse curve to the entrance of the tubular outlet forming a venturi, whereby the air is directed in stream lines from the intake of the body to the tubular outlet leading to the carburetor.

.2. A back firetrap for internal combustion engines comprising a body for attachment to the air intake of the carburetor of the engine, the body being open at one end for the intake of air and the outlet of back fire gases and having a tubular outlet at. its other end connectible to the intake of the carburetor, the open intake end being of greater diameter than the tubular outlet, means in the intake opening for cooling the back fire gases, the walls of the body between the intake end and the tubular outlet curving in an outward curve from the intake end toward the tubular outlet to the intermediate part of the body and then curving in an in-' ward reverse curve to the entrance of the tubular outlet, said outward curve being of lesser radius of curvature than said inward reverse curve forming a passage whereby the airis directed in stream lines from the intake of the body to the tubular outlet leading to the carburetor.

ORSON A. CARNAHAN. 

